Several problems exist with the utilization of separate cellular and Voice-over-IP (VoIP) solutions. First, consumers often are forced to deal with the inconvenience of managing multiple numbers for home, office and travel. Having multiple phone numbers, mailboxes, and places for setting communication preferences can be confusing and require additional effort to make sure that all messages are received and all missed calls are known.
Second, the airtime charges associated with cellular calls can be significant. This is wasteful given that many cellular telephone calls occur from either the office or the home, areas that have an increasing likelihood of being WiFi hotspots. It is especially wasteful in the context of international roaming charges which are frequently more costly than calling within a domestic coverage area.
Third, many cellular companies have coverage problems, especially in rural areas and in buildings, where WiFi is often found. Lastly, current cellular infrastructure requires expensive upgrades to support higher bit rate services and applications that customers want.
Fixed Mobile Convergence (FMC) services is the integration of wireless and wireline technology to create a single converged network that allows wireless users to access services on both wireless and wireline infrastructure through a single handset. There are two basic strategies for implementing FMC, namely Unlicensed Mobile Access (UMA) and IP Multimedia Subsystem (IMS). UMA is considered a simpler gateway-based access convergence implementation, while IMS is a more complex, server-based service convergence implementation. IMS also has much broader goals and is intended for true service convergence across all types of access networks and user device. Hence IMS-based solutions are both complex and expensive for many smaller operators who want FMC but do not want to incur the high cost of deployment.
Both UMA and IMS solutions provide access to various services through Wireless LAN (WLAN-802.11b/g) or WiFi, using special dual-mode handsets. They are intended to provide enhanced cellular coverage in rural and poorly served areas, overcome reception problems within buildings, offer higher data rates and reduce airtime charges by taking advantage of WiFi infrastructure that is ubiquitously deployed in many homes and public places (both for calls within a domestic plan as well as calls that would otherwise be charged at international roaming rates). New dual-mode handsets offered by cell phone makers automatically select between WiFi Mode and Cellular Mode of operation based on network availability. If both networks are available, then WiFi Mode is given preference over Cellular Mode.
To date, implementation trials of FMC have mainly relied on IP Multimedia Subsystem (IMS) standards and architectures. In this respect, IMS is viewed as unifying service delivery architecture for wireline and wireless services.
UMA-based approaches have also been proposed but have required tunneling cellular network signals over WiFi networks. This has several disadvantages. They include that (1) the VoIP network is not leveraged such that traditional Inter-Machine Trunks (IMT) and cell resources are still used and (2) additional value-added services utilizing the available WiFi resources are not provided.
While some of these issues may be addressed to some degree by adding IMS network elements into the core of the cell network, that level of integration is very invasive, and may include modifying data records in the core customer database, the Home Location Registrar (HLR). Those types of modifications can be harmful and error-prone.